Pneumatic power-unit having a driving piston and an exhaust valve

ABSTRACT

An improved pneumatic power unit is provided including a penumatic piston reciprocally operable within an operating cylinder housing, which, in one conceivable application, operates the contact structure of a power circuit-breaker, and uses a normally-open three-way valve, which normally provides highpressure gas on both sides of the driving piston within the operating cylinder housing. During the closing operation of the circuit-breaker, when the pneumatic power unit of the instant invention is applied to this particular application, the threeway normally-open valve is operated to exhaust one side of the driving piston, and the high-pressure gas already present on the other side of the piston provides the required closing force to close the contacts of the circuit-breaker against the usuallyprovided accelerating spring pressure tending to open the breaker. The de-energization of the normally-open three-way valve returns the closing or driving piston to its normal reset position, in such a particular application, thus not requiring a return spring, since the cross-sectional area of the piston-shaft is acted upon by the internal high-pressure gas present on the return or non-working side of the piston assembly in the cylinder housing, and since normal atmospheric air pressure obviously exists on the outside or externally of the operating-cylinder housing thereby exerting relatively little inward force on the cross-sectional area of the piston rod.

United States Patent 'Rostron et al.

[ Dec. 30, 1975 Assignee: Westinghouse Electric Corporation,

Pittsburgh, Pa.

[22] Filed: Sept. 27, 1973 [2]] Appl. N0.: 401,520

[52] US. Cl. 200/82 B; 200/83 A; 200/148 F; 91/416; 137/625.64 [51] Int.Cl. H0111 35/38 [58] Field of Search 335/174, 191; 200/82 R, 200/82 B,82 C, 169 R,145, 153 G, 153 V, 153 H, 148 E, 148 F, 83 A, 83 C, 83 J;137/625.64; 91/416 [56] References Cited UNITED STATES PATENTS 2,667,554l/l954 Shores 200/148 F 3,334,202 8/1967 Tognella... 200/153 H 3,438,2464/1969 Lotti 200/82 R 3,591,051 7/1971 Mitchell 200/83 A 3,624,32911/1971 Fischer 200/148 F 3,646,292 2/1972 Barkan 200/82 B 3,766,53610/1973 Hile 200/83 A 3,766,834 10/1973 Kraemer 200/83 C 3,780,52812/1973 Brandenburg... 200/83 A FOREIGN PATENTS OR APPLICATIONS 915,8581/1963 United Kingdom I? E 23 N as "Q 65 N;

4o 4 2 nnna 32 l l Primary Examiner-Gerald P. Tolin Attorney, Agent, orFirmW. R. Crout [57] ABSTRACT An improved pneumatic power unit isprovided including a penumatic piston reciprocally operable within anoperating cylinder housing, which, in one 'conceivable application,operates the contact structure of a power circuit-breaker, and uses anormallyopen three-way valve, which normally provides highpressure gason both sides of the driving piston within the operating cylinderhousing. During the closing operation of the circuit-breaker, when thepneumatic power unit of the instant invention is applied to thisparticular application, the three-way normally-open valve is operated toexhaust one side of the driving piston, and the high-pressure gasalready present on the other side of the piston provides the requiredclosing force to close the contacts of the circuit-breaker against theusually-provided accelerating spring pressure tending to open thebreaker.

16 Claims, 4 Drawing Figures CLOSED POSITION OF BKR, PISTON RESET US.Patent Dec. 30, 1975 Sheet10f3 3,930,134

w 0N m U.S. Patsnt Dec. 30, 1975 Sheet 2 of3 3,930,134

ZOELmOQ ZmEO omanzwtl U.S. Patent Dec.30, 1975 Sheet3of3 3,930,134

CROSS-REFERENCES TO RELATED APPLICATIONS Applicants are not aware of anyrelated patent applications pertinent to the present invention.

BACKGROUND OF THE INVENTION In U.S. Pat. No. 3,624,329, issued Nov. 30,1971 to William H. Fischer et al, and assigned to the assignee of theinstant application, there is illustrated and described a pneumaticoperating mechanism for a circuitinterrupter in which a spring-retrievedclosing piston is pneumatically operated to rotate a circuit-breakerclosing lever and thereby to close the breaker contacts. Upon theremoval of pressure from the closing piston, a compression Spring,located within the operating cylinder, retrieved the closing or drivingpiston to thereby disengage the piston-rod from a roller associated withthe rotatable operating lever. The closing piston utilized anormally-closed three-way valve, and the valve provided the piston withlow pressure on the working side of the closing piston in its resetposition. The working side of the piston was pressurized by operation ofthe three-way valve to provide the requisite closing force on the pistonto close the breaker. In addition, there was a compression springprovided in the closing cylinder on the non-working side of the pistonto return the piston to its reset position, so that the piston did notinterfere with the tripping operation of the breaker after a closingoperation had been accomplished. Also, a latch-check switch de-energizedthe solenoid valve after the mechanism was completely closed, and, inaddition, a switch was required to prevent tripping of thecircuit-breaker until the driving piston had been returned to itsoriginal reset position.

The present invention is particularly concerned with an improvedpneumatic power unit having wide application, with one particularapplication concerned with a circuit-breaker operating mechanismoperable to effect the closing operation of a power circuit-breakeragainst heavy accelerating opening spring pressures tending to open thebreaker contacts, and yet having the piston in a position out of the wayduring a subsequent tripping operation in the normal latched-closedposition of the breaker. The invention is particularly suitable for theoperating mechanisms of power circuitbreakers of relatively high-voltageand high-current carrying capacity.

SUMMARY OF THE INVENTION In accordance with the present invention, thereis provided an improved pneumatic power unit having wide application,one particular application being its use with an operating mechanismassembly operable to close the circuit-breaker contacts of a powercircuitbreaker by piston action, which involves a normallyopen three-waycontrol valve which exhausts one side of the driving piston to providethe power-closing stroke for the mechanism.

To effect a retrieving action of the piston, the threeway control valveis de-activated or de-energized, and thus provides high pressure on bothsides of the driving piston. Due to the differential pressure actingacross the cross-sectional area of the piston-shaft extending out of theoperating cylinder, with high-pressure gas 2 existing on the non-workingside of the piston, and normal atmospheric air pressure existing on theoutside of the piston-operating cylinder, there is provided therequisite differential pressure force across the pistonrodcross-sectional area to effect the return of the piston to its normalde-activated reset position with pressure existing on both sides of thedriving piston. At this time, the normally-open three-way control valveis in its de-energized position.

Further advantages will be apparent upon reading the followingspecification taken in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional viewillustrating the improved pneumatic power unit of the circuit-breaker inthe contact-closed position with the piston assembly in its retrievedreset position;

FIG. 2 is a view similar to that of FIG. 1, but illustrating thecircuit-breaker in its tripped open position;

FIG. 3 illustrates the position of the several parts during apower-closing stroke of the circuit-breaker mechanism; and,

FIG. 4 is an end sectional view taken substantially along the line IVIVof FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings, andmore particularly to FIG. 1, it will be observed that there is providedan operating mechanism, generally designated by the reference numeral 1,operable to effect the closing and opening operations of thecircuit-breaker contacts 2, 3 and 4 of a power circuit-breaker 5. Thethree sets of circuit-breaker contacts 2, 3 and 4 are diagrammaticallyillustrated in FIG. 1, inasmuch as the present invention is particularlyconcerned with the circuitbreaker operating mechanism 1. The particularoperating mechanism 1 is associated, for example, with a powercircuit-breaker 5 of the type set forth in U.S. Pat. No. 3,624,329,issued Nov. 30, 1971, to William H. Fischer et al, and assigned to theassignee of the instant application. Although the view in FIG. 1 shows adirect mechanical connection to the contacts, the mechanism mayalternatively operate control valves, the latter in turn controlling gasflow to pistons which are linked to the contacts as in U.S. Pat. No.3,624,329. Reference may be made to this patent for backgroundinformation regarding certain structural component parts of the powercircuit-breaker, if desired. Since the present invention is particularlyconcerned with the operating mechanism 1, however, the contact structurehas been simplified, and is, as shown, diagrammatically illustrated inFIG. 1 of the drawings.

A trip-magnet assembly 7 is provided for releasably magneticallylatching the circuit-breaker 5 in the closed position. As set forth inthe aforesaid patent, generally, the trip-magnet assembly 7 comprises aholding-magnet 11 and a trip-lever l3, pivotally mounted upon astationary pivot 15, and having its tail portion 17 maintain atoggle-linkage 19 in a slightly underset condition. As shown in FIG. 1,the toggle-linkage 19 comprises a pair of toggle-links 21, 23 one togglelink 21 being pivotally mounted upon a stationary pivot 25, and theother toggle link 23 being pivotally connected to a moving pivot 27 atthe outer free end of a main operating lever assembly, generallydesignated by the reference numeral 29, and pivotally mounted upon a 3stationary pivot 30.

An operating rod 31 is pivotally connected intermediate the ends of themain operating lever-assembly, as at 32, and is also connected to themovable contacts 2a, 3a, 4a of the circuit-breaker 5, diagrammaticallyillustrated, which are under heavy spring pressure 34 in theclosed-circuit position of the interrupter tending to effect theiropening operation, as shown in FIG. 1. In more detail one or moreaccelerating springs 34 are interposed between a stationary cross-plate36 extending across and affixed, as by welding, for example, to twoheavy side support plates 38, which journal the various stationary pivotpins 25, 30, and 37 of the mechanism 1. The other end of the compressionspring 34 bears upon a movable spring-plate 40 affixed to and movablewith the contact operating rod 31.

A pair of bumpter assemblies 42 and 43 are provided to cushion the endsof the opening and closing movements of the main operatinglever-assembly 29; and an auxiliary switch assembly 44 is provided,being connected through a bell-crank lever 46 and a link 48 to a portion50 of the main operating lever-assembly 29 to provide the desiredactuation of the auxiliary switch 44. As well known by those skilled inthe art, the auxiliary switch 44 controls electrical circuits (notshown), which are responsive to the open and closed-circuit positions ofthe interrupter 5.

As illustrated in FIG. 1, the main operating leverassembly 29 is underspring pressure 34 to open the contacts 2, 3 4, but is maintained in itsclosed position, as shown in FIG. 1, under such spring pressure 34 bythe latching action of the trip-magnet assembly 7. Trip coils 52, 53 areassociated with the magnet assembly 7, and when energized, divert themagnetic flux within the holding magnet 11 and thereby effect therelease of the armature, or keeper 55, which in turn, will permitcollapse of the toggle-linkage l9 and thereby allow springopeningoperation of the contacts 2a, 3a, 4a of the cirucit-breaker 5.

To effect the closing operation of the circuit-breaker 5, there isprovided an improved closing-piston assembly 57, including a drivingpiston 59 reciprocally operable interiorly of a pneumatic operatingcylinder 60 normally having high-pressure air, or gas 61 on both sidesthereof. The fluid 61 may, of course, be other than air, and, in fact,may be any suitable gas, even a gas suitable for arc-extinguishingpurposes in the breaker 5. This is particularly true where thecircuitbreaker is one of the sulfurhexafluoride (SF type, in which it isnot desired to utilize two separate gases, such as SF gas and compressedair, in the same breaker installation 5. Thus, the sulfurhexafluoridegas 61 may not only be used for arc-extinguishing purposes at thecontacts 2, 3, 4, but in fact is used for the pneumatic operation of thedriving piston-assembly 57.

It will be observed that the driving piston 59 is interconnected with apiston rod 63, which has an actuatingend portion 65 with a longitudinalslot 67 provided therein. This provides a lost-motion connection 64between the rod 63 and the roller 68 carried by the lever 29. When thecircuit-breaker 5 is in the opencircuit position, as illustrated in FIG.2, it will be observed that the roller 68, movable with the mainoperating lever assembly 29, is in a position close to the end 67a ofthe elongated slot 67. In this event, exhausting of gas 61 from therighthand end 71 of the piston cylinder 60 will permit the high-pressuregas 61 on the left-hand working face 73 of the drivinging piston 59 toeffect a rightward closing operation of the driving piston 59, andthereby forcibly carry the roller 68 and hence the main operatinglever-assembly 29, in a clockwise direction, as viewed in FIGS. 2 and 3,to thereby effect a closing operation of the interrupter 5. FIG. 3 showssuch a power-closing operation of the circuit breaker 5 in a moredetailed manner.

The present invention is suitable for use with any conventional,normally-open, three-way control valve 75, which when operated, willexhaust the region 71 on the right-hand non-working face of the drivingpiston 59. Deenergization of the normally-open three-way control valve75, high-pressure gas 61 is again permitted to flow through the piping77, 78 and into the righthand chamber 71 of the operating cylinder 60and the consequent equalization of gas pressure on both sides of thepiston 59 will drive the piston assembly 59 to its leftward end resetposition, as shown in FIG. 1, by virtue of the differential pressureexisting on the piston assembly 59. As well known by those skilled inthe art, this differential pressure exists because of the crosssectionalarea A (FIG. 4) of the piston-rod 63 itself. Thus, with reference to thecross-sectional area A (FIG. 4) of the piston-rod 63, it will beobserved that there is high-pressure gas 61 acting to force thepistonrod 63 leftwardly out of the operating cylinder 60, as viewed inFIG. 1, whereas there is merely atmospheric pressure, or low-pressuregas, externally of the operating cylinder 60. An unbalanced pressureforce upon the piston rod 63 of the piston-assembly 59 consequentlyexists.

The equalization of gas pressure on both sides of the piston 59 will, asmentioned, force the piston 59 to the left to be ultimately arrested atan annular stop designated by the reference numeral 72.

High-pressure gas 61 is constantly supplied to the operating cylinderspace 76 by a high-pressure supply pipe 81 fed from a suitablehigh-pressure reservoir 85.

To prevent leakage of gas 61 out of the pneumatic operating cylinder 60,there is provided a syIphon-bellows 80, for example, to prevent leakageof gas along the opening 82 provided in the end plate 84 of theoperating cylinder 60. The present invention, of course, is not limitedto the use of a sylphon-bellows 80, but any good seal may be provided,as desired. The use of a sylphon-bellows 80, of course, assures thatlong operational life will be obtained with no leakage occurring alongthe opening 82 in the end head-plate 84 of the operating cylinder 60.

The electrical control 86 for the actuation of the three-way pneumaticcontrol valve is illustrated in FIG. 1, and it will be observed thatupon pressing or closing the close button 88, the control valve 75 willbe actuated, and will thereby exhaust the region 71 on the right-handnon-working face 90 of the driving piston 59. This will, of course,permit the normally-present high-pressure gas 61 in the region 76 on thelefthand working face 73 of the driving piston 59 to drive thepiston-rod 63 to the right, and thereby effect closing of the circuitbreaker 5. The closed position of the contacts 2, 3, 4 of thecircuitbreaker 5, of course, is resisted by accelerating springs 34normally provided in circuit-breaker structures to assist in asubsequent quick-opening operation of the contacts.

From the foregoing description, it will be apparent that there has beenprovided an improved closing-piston assembly 57 for a circuit-breakermechanism 1, which utilizes a normally-open three-way valve 75. The

normally-open three-way valve 75 provides high-pressure gas on bothsides of the driving piston 59. The valve 75 exhausts one side 71 of thedriving piston 59, and the high-pressure gas 61 on the other side 76 ofthe driving piston 59 provides the required closing force to close thebreaker. The return of the drivng piston 59 to its normal resetposition, as shown in FIG. 1, does not require a spring. As mentioned,the area A (FIG. 4) of the piston-shaft 63 with high-pressure gasexisting on the inside of the piston assembly 61 in the region 71, andnormal atmospheric air pressure existing on the outside of the operatingcylinder 60, provides the re quired force to return the driving piston59 to its end leftward reset position, as shown in FIGS. 1 and 2.

The valving arrangement is calculated and has been observed to be veryconsistent in its operation over a wide range of pressures. Thisconsistency allows the usual latch-check switch to be deleted, and thevalve to be deenergized by the auxiliary contacts that are required forother functions as well. The switch formerly used to assure that thedriving piston 59 is fully returned prior to a trip operation is alsoeliminated, due

to the consistency of operation of the mechanism 1.

The full return stroke of the driving piston 59 prior to a tripoperation can be assured without the use of this switch.

Although there has been illustrated and described a specific structure,it is to be clearly understood that the same was merely for the purpose-of. illustration, and that changes and modifications may readily bemade therein by those skilled in the art, without departing from thespirit and scope of the invention.

We claim:

1. An operating mechanism for a circuit-interrupter including incombination:

a. means defining separable contact means;

b. a movable member;

c. means rendering opening and closing motions of said separable contactmeans responsive to the movement of said movable member (29);

d. a pneumatic operator including a driving-piston operable within apneumatic operating cylinder and having a piston-rod extendingexternally out of said pneumatic operating cylinder;

e. said piston rod being connected with said movable member (29) tocause the actuation thereof;

f. said piston-rod extending only out of one end of the operatingcylinder on one working side of the driving piston;

g. the other end of the operating cylinder on the nonworking side of thepiston being closed with respect to the piston-rod;

h. valve means normally maintaining high-pressure gas within saidpneumatic operating cylinder on both the driving and non-driving sidesof the driving-piston to thereby extend the piston-rod outwardly bydifferential piston action; and,

. means for operating said valve means and exhausting gas from thenon-driving side of the driving-piston at said other end of the cylinderto thereby move the driving-piston toward the closed end of theoperating cylinder and the movable member (29) to close the breakercontacts.

2. The combination according to claim 1, wherein the movable member is arotatable main operating lever pivotally mounted upon a stationary pivotand connected to said piston-rod.

3. The combination according to claim 2, wherein the connection betweenthe piston-rod and the rotatable main operating lever is a lost-motionconnection, whereby the driving-piston may assume its reset positionwithout interference with the rotatable main operating lever.

4. The combination according to claim 1, wherein a collapsibletoggle-linkage releasably maintains the movable member in its closedposition.

5. The combination according to claim 4, wherein a holding meansincluding a magnetically-actuated trigger-arm maintains the collapsibletoggle-linkage in an underset condition.

6. The combination according to claim 1, wherein opening acceleratingspring means tends to bias the movable contacts of thecircuit-interrupter in the opening direction, and a lost-motionconnection is provided between the movable member and the piston-rod ofthe pneumatic operator.

7. The combination according to claim 1, wherein the valve meansincludes a normally-open three-way control valve, and the movable membercomprises a rotatable operating lever pivotally mounted upon astationary pivot and having a lost-motion connection with the piston-rodofthe pneumatic operator.

8. The combination according to claim 3, wherein the lost-motionconnection is an elongated slot provided in the piston-rod.

9. The combination according to claim 1, wherein the normal resetposition of the driving-piston with high-pressure gas existing on bothsides thereof is intermediate the ends of the pneumatic operatingcylinder and against a stop portion provided on the pneumatic operatingcylinder.

10. A pneumatic power-unit including, in combination:

a. means defining an operating cylinder;

b. a driving piston operable within said operating cylinder andresponsive to the gas-pressure conditions existing therewithin;

c. a piston-rod fixedly secured to and movable with said driving pistonand responsive to the movement thereof;

d. said piston-rod projecting externally of said operating cylinder atone end thereof through a first open cylinder-head and having aneffective crosssectional area of A;

. a first pneumatic region (76) defined by said driving piston, theinner side walls of the operating cylinder and said first opencylinder-head of the operating cylinder at said one end of the operatingcylinder;

f. a second pneumatic region (61) disposed on the other side of saidoperating piston from said first pneumatic region;

g. high-pressure gas conditions existing in said first pneumatic regionat all times during operation of the pneumatic power unit;

h. operating means including a three-way control valve for alternatelypressurizing or exhausting said second pneumatic region;

i. the pressurization level of said second pneumatic region beingsubstantially at the same gas-pressure level as said constant-pressuregas-level of the first pneumatic region; and,

j. the cross-sectional area A of said piston-rod being of sufficientadequate cross-sectional area to rapidly retract, by differential pistonaction, the

operating movement of the operating piston toward said one end of theoperating cylinder, whereby pressurization of the second pneumaticregion will operatively move the piston-rod toward said first opencylinder-head of the operating cylinder, and exhausting of the secondpneumatic region by operation of said control-valve will correspondinglyeffect driving inward motion of the operating piston and the piston-rodtoward the other or closed second cylinder-head for retracting purposesof the operating piston.

11. The combination of claim 10, wherein stop means for the operatingpiston is provided along the inner side wall of the operating cylinder.

12. The combination in a circuit-breaker of separable contacts separableto establish arcing, means biasing said separable contacts to theopen-circuit position, a closing mechanism for effecting the closing ofsaid separable contacts including a pneumatic operator, said pneumaticoperator including a driving-piston operable within a pneumaticoperating cylinder, a rotatable main lever pivotally mounted upon astationary pivot, a piston-rod connected to said driving-piston andhaving a lost-motion mechanical connection with said rotatable mainlever, said piston-rod projecting externally of said operating cylinderat one end thereof through a first open cylinder-head and having aneffective cross-sectional area of A, a first pneumatic region (76)defined by said driving-piston, the inner sidewalls of the operatingcylinder and said first open cylinder-head of the operating cylinder atsaid one end of the operating cylinder, a second pneumatic region (61)disposed on the other side of said operating piston from said firstpneumatic region, high-pressure gas conditions existing in said firstpneumatic region at all times during operation of the pneumaticoperator, operating means including a three-way control-valve foralternately pressurizing or exhausting said second pneumatic region, thepressurization level of said second pneumatic region being substantiallyat the same gaspressure level as-said constant-pressure gas-level of thefirst pneumatic region, the cross-sectional area A of said piston-rodbeing of sufficient adequate cross-sectional area to rapidly retract bydifferential pressureaction the operating movement of the operatingpiston toward said one end of the operating cylinder, wherebypressurization of the second pneumatic region will operatively move thepiston-rod toward said first open cylinder-head of the operatingcylinder, and exhausting of the second pneumatic region by operation ofsaid three-way control-valve will correspondingly effect inward drivingmotion of the operating piston and the piston rod toward the other orclosed second cylinderhead for retracting purposes of thedriving-piston, and said retracting movement of the driving-piston andsaid lost-motion connection will locate the piston-rod in anon-interfering position relevant to the rotatable main lever.

13. The combination according to claim 12, wherein the valve meanscomprises a three-way pneumatic control valve, said rotatable main leveris releasably maintained in its closed position by a collapsibletoggle-linkage, and said collapsible toggle-linkage is maintained in anunderset condition by a releasable holding means.

14. The combination according to claim 12, wherein the valve meanscomprises a three-way pneumatic control valve, said rotatable main leveris releasably maintained in its closed position by a collapsibletogglelinkage, and said collapsible toggle-linkage is maintained in anunderset condition by a releasable holding means.

15. The combination according to claim 14, wherein the releasableholding means comprises a magneticallyactuated trigger-arm.

16. The combination according to claim 15, wherein a pair ofshock-absorbers cushion the opening and closing motions of the rotatablemain operating lever.

1. An operating mechanism for a circuit-interrupter including incombination: a. means defining separable contact means; b. a movablemember; c. means rendering opening and closing motions of said separablecontact means responsive to the movement of said movable member (29); d.a pneumatic operator including a driving-piston operable within apneumatic operating cylinder and having a piston-rod extendingexternally out of said pneumatic operating cylinder; e. said piston rodbeing connected with said movable member (29) to cause the actuationthereof; f. said piston-rod extending only out of one end of theoperating cylinder on one working side of the driving piston; g. theother end of the operating cylinder on the nonworking side of the pistonbeing closed with respect to the piston-rod; h. valve means normallymaintaining high-pressure gas within said pneumatic operating cylinderon both the driving and nondriving sides of the driving-piston tothereby extend the piston-rod outwardly by differential piston action;and, i. means for operating said valve means and exhausting gas from thenon-driving side of the driving-piston at said other end of the cylinderto thereby move the driving-piston toward the closed end of theoperating cylinder and the movable member (29) to close the breakercontacts.
 2. The combination according to claim 1, wherein the movablemember is a rotatable main operating lever pivotally mounted upon astationary pivot and connected to said piston-rod.
 3. The combinationaccording to claim 2, wherein the connection between the piston-rod andthe rotatable main operating lever is a lost-motion connection, wherebythe driving-piston may assume its reset position without interferencewith the rotatable main operating lever.
 4. The combination according toclaim 1, wherein a collapsible toggle-linkage releasably maintains themovable member in its closed position.
 5. The combination according toclaim 4, wherein a holding means including a magnetically-actuatedtrigger-arm maIntains the collapsible toggle-linkage in an undersetcondition.
 6. The combination according to claim 1, wherein openingaccelerating spring means tends to bias the movable contacts of thecircuit-interrupter in the opening direction, and a lost-motionconnection is provided between the movable member and the piston-rod ofthe pneumatic operator.
 7. The combination according to claim 1, whereinthe valve means includes a normally-open three-way control valve, andthe movable member comprises a rotatable operating lever pivotallymounted upon a stationary pivot and having a lost-motion connection withthe piston-rod of the pneumatic operator.
 8. The combination accordingto claim 3, wherein the lost-motion connection is an elongated slotprovided in the piston-rod.
 9. The combination according to claim 1,wherein the normal reset position of the driving-piston withhigh-pressure gas existing on both sides thereof is intermediate theends of the pneumatic operating cylinder and against a stop portionprovided on the pneumatic operating cylinder.
 10. A pneumatic power-unitincluding, in combination: a. means defining an operating cylinder; b. adriving piston operable within said operating cylinder and responsive tothe gas-pressure conditions existing therewithin; c. a piston-rodfixedly secured to and movable with said driving piston and responsiveto the movement thereof; d. said piston-rod projecting externally ofsaid operating cylinder at one end thereof through a first opencylinder-head and having an effective cross-sectional area of ''''A'''';e. a first pneumatic region (76) defined by said driving piston, theinner side walls of the operating cylinder and said first opencylinder-head of the operating cylinder at said one end of the operatingcylinder; f. a second pneumatic region (61) disposed on the other sideof said operating piston from said first pneumatic region; g.high-pressure gas conditions existing in said first pneumatic region atall times during operation of the pneumatic power unit; h. operatingmeans including a three-way control valve for alternately pressurizingor exhausting said second pneumatic region; i. the pressurization levelof said second pneumatic region being substantially at the samegas-pressure level as said constant-pressure gas-level of the firstpneumatic region; and, j. the cross-sectional area ''''A'''' of saidpiston-rod being of sufficient adequate cross-sectional area to rapidlyretract, by differential piston action, the operating movement of theoperating piston toward said one end of the operating cylinder, wherebypressurization of the second pneumatic region will operatively move thepiston-rod toward said first open cylinder-head of the operatingcylinder, and exhausting of the second pneumatic region by operation ofsaid control-valve will correspondingly effect driving inward motion ofthe operating piston and the piston-rod toward the other or closedsecond cylinder-head for retracting purposes of the operating piston.11. The combination of claim 10, wherein stop means for the operatingpiston is provided along the inner side wall of the operating cylinder.12. The combination in a circuit-breaker of separable contacts separableto establish arcing, means biasing said separable contacts to theopen-circuit position, a closing mechanism for effecting the closing ofsaid separable contacts including a pneumatic operator, said pneumaticoperator including a driving-piston operable within a pneumaticoperating cylinder, a rotatable main lever pivotally mounted upon astationary pivot, a piston-rod connected to said driving-piston andhaving a lost-motion mechanical connection with said rotatable mainlever, said piston-rod projecting externally of said operating cylinderat one end thereof through a first open cylinder-head and having aneffective cross-sectional area of ''''A'''', a first pneumatic region(76) defined by said driving-piston, the inner side-walls of theoperating cylinder and said first open cylinder-head of the operatingcylinder at said one end of the operating cylinder, a second pneumaticregion (61) disposed on the other side of said operating piston fromsaid first pneumatic region, high-pressure gas conditions existing insaid first pneumatic region at all times during operation of thepneumatic operator, operating means including a three-way control-valvefor alternately pressurizing or exhausting said second pneumatic region,the pressurization level of said second pneumatic region beingsubstantially at the same gas-pressure level as said constant-pressuregas-level of the first pneumatic region, the cross-sectional area''''A'''' of said piston-rod being of sufficient adequatecross-sectional area to rapidly retract by differential pressure-actionthe operating movement of the operating piston toward said one end ofthe operating cylinder, whereby pressurization of the second pneumaticregion will operatively move the piston-rod toward said first opencylinder-head of the operating cylinder, and exhausting of the secondpneumatic region by operation of said three-way control-valve willcorrespondingly effect inward driving motion of the operating piston andthe piston rod toward the other or closed second cylinder-head forretracting purposes of the driving-piston, and said retracting movementof the driving-piston and said lost-motion connection will locate thepiston-rod in a non-interfering position relevant to the rotatable mainlever.
 13. The combination according to claim 12, wherein the valvemeans comprises a three-way pneumatic control valve, said rotatable mainlever is releasably maintained in its closed position by a collapsibletoggle-linkage, and said collapsible toggle-linkage is maintained in anunderset condition by a releasable holding means.
 14. The combinationaccording to claim 12, wherein the valve means coomprises a three-waypneumatic control valve, said rotatable main lever is releasablymaintained in its closed position by a collapsible toggle-linkage, andsaid collapsible toggle-linkage is maintained in an underset conditionby a releasable holding means.
 15. The combination according to claim14, wherein the releasable holding means comprises amagnetically-actuated trigger-arm.
 16. The combination according toclaim 15, wherein a pair of shock-absorbers cushion the opening andclosing motions of the rotatable main operating lever.